Interactions between cells and the substrate to which they attach are important for many biological processes, including control of growth and differentiation. Loss or aberration of normal response in cancer cells to adhesive factors of the cell substratum may be involved in several ways in neoplastic growth, malignant invasion, and metastasis. Recently we have studied, as a model for cell-substratum interactions, a 70,000-kilodalton-adhesive glycoprotein isolated from human serum, which we termed "serum spreading factor" (SSF). We developed a bank of monoclonal antibodies which we used in the characterization of biochemical properties and biological activities of SSF. Further progress is as follows: (1) we have developed a four-step isolation procedure for SSF employing sequential chromatography on columns of glass beads, concanavalin A, DEAE, and heparin; (2) using our monoclonal antibodies, we have adopted previously developed immunoassay procedures for the quantitative immunoassay of SSF, allowing us to estimate the amount of SSF in mixtures of proteins, including SSF in serum, plasma, or tissue, and cell culture extracts; (3) in an approach to determining which components of serum are important to the attachment and spreading of cells in culture, we have used glass bead affinity chromatography, the procedure used in the first step of SSF purification from serum, to deplete simultaneously serum of SSF, fibronectin, and cell spreading-promoting activity; and (4) we have found sequence analysis of the amino-terminal portion of purified SSF indicates identity in this region with somatomedin B, a 5,000-kilodalton peptide of human plasma. Further studies in progress include: (1) large-scale purification of SSF from human serum in order to determine precisely biochemical properties of the protein; (2) studies on the mechanism of action of spreading factors promoting cell proliferation; and (3) studies of the ability of human cells in vitro to synthesize spreading factor, regulatory molecules affecting synthetic capacity and secretion, and the nature of the molecule produced. (A)